IRJET- Experimental and Analytical Investigation of Concrete Beam Reinforced with Hybrid Bars (Steel

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EXPERIMENTAL AND ANALYTICAL INVESTIGATION OF CONCRETE BEAM REINFORCED WITH HYBRID BARS (STEEL AND GFRP) G. Ganesh kumar1, J. Herbert Sinduja2 1,2Assistant

Professor, Department of civil Engineering, Jerusalem College of Engineering, Pallikaranai ------------------------------------------------------------------------***------------------------------------------------------------------------Abstract: In this paper, the results of experimental and analytical investigation of flexural behaviors of concrete beams reinforced with glass-reinforced-polymer (GFRP) bars were studied. The GFRP rebar having the tensile strength of 902 MPa and Young’s modulus of 46 GPa. The beams were 1800 mm long with a rectangular cross section of 150 mm in width and 200 mm in depth. Totally Four beams were tested.

One beam was reinforced with glass-FRP bars, two beams were reinforced with both glass-FRP bars and steel and one was reinforced with steel, serving as a control specimen. The beams were tested to failure in four-point bending over a clear span of 1600 mm. The test results were reported in terms of ultimate load carrying capacity, deflection and cracks. The experimental results were used to predict the load vs. deflection of Concrete beams reinforced with hybrid bars. The measured load vs. deflections was analyzed and compared with the predicted FEM model using ABAQUS. The results indicate that the reaction forces and deflections obtained from the finite element model (FEM) were well matched with the experimental results.

FRP bars are considered as an alternative to the steel reinforcements in concrete structures, especially in aggressive environments, because of their high strength to weight ratio and non-corrodible nature. The performances of concrete beams reinforced with FRP bars have been studied in many countries and have issued design codes or guides for FRP-reinforced concrete structures [Japan Society of Civil Engineers (JSCE) 1997; Canadian Standard Association (CSA) 2002; American Concrete Institute (ACI) 2006; (CSA) 2006].

Key words: GFRP, ABAQUS, finite element, fiber reinforced polymer, reinforced concrete beam.

1.1 GFRP Rebar

In this paper, we investigated the load vs. deformation of hybrid GFRP/steel-reinforced concrete beams both analytically and experimentally. Our analytical model is done by using ABAQUS to predict the load vs. deflection relationship of the beams. Design models for predicting flexural strength, and deflection are presented. We tested beams with different reinforcement ratios of GFRP to steel, and compared the experimental results with the analytical predictions.

Glass Fiber Reinforced Polymers are a proven and successful alternative that have numerous advantages over traditional reinforcement methods, giving structures a longer service life. The GFRP rebar is a structural ribbed reinforcing bar made of high strength and corrosion resistant glass fibers that are impregnated and bound by an extremely durable polymeric epoxy resin. This combination equals an engineered material system resulting in unique attributes that replace and supersede typical materials such as galvanized, epoxy coated and stainless steel rebar. Its characteristic properties are ideal for any harsh and corrosive environments. GFRP is permanently resistant to chemical acids and alkaline bases, therefore extra concrete cover, anti-shrink additives, and even cathodic protection are not required. GFRP significantly improves the longevity of engineering structures where corrosion is a major factor.

1. INTRODUCTION The durability of concrete structures has been a great concern. Most common problems are arising in durability relating to the corrosion of steel reinforcement in concrete structures. Coastal structures, chemical industries, ports and bridges are the examples of structure subjected to corrosion of steel reinforcement. Corrosion doesn’t begin simultaneously in all steel bars in concrete. Corrosion starts in the corner areas of the structure, for the following reasons (Qu and Zhang 2001): (1) a high carbonation rate; (2) easy entry of oxygen and water content; and (3) lower resistance to spalling than in other parts of the cross section. Corrosion starts to spall the concrete around the corner area first, and following accelerates the corrosion of inner steel reinforcements. The resistance of reinforced concrete (RC) to corrosion can be enhanced by improving the concrete quality, increasing the concrete cover, and replacing the steel bars located in the corner areas of the cross section by non-corrodible materials such as fiberreinforced polymer bars.

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GFRP will not rust, even in the harshest environments. It does not react to salt ions, chemicals or the alkaline present in concrete. GFRP rebar offers a tensile strength up to 3 times that of steel. GFRP is highly efficient to resisting heat transfer applications and does not create a thermal bridge within structures. GFRP rebar does not contain any metal; it will not cause any interference in contact with

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strong magnetic fields or when operating sensitive electronic instruments such as MRI units and rooms, Communications, Airports, Transformers, Aluminum and Copper Smelting Plants, Tele-Communications towers, Airport control towers, Hospitals and Rail roads. GFRP rebar is 9 times lighter in weight than the equivalent strength of Steel rebar. It is much easier to handle, and in most cases, only one truck load will be sufficient to supply the rebar even for an entire project.

approach; this model can help to confirm the laboratory investigation behavior. For validation, a reinforced concrete beam was modeled which had been experimentally tested. This is followed by a comparison of the finite element results with experimental results on RC beam elements in the following study.

2. EXPERIMENTAL PROGRAM 2.1. Test specimen and materials The summary of the experimental work conducted in the present investigation to study the loads vs. deflection with different reinforcement ratios. Totally four beams were tested. One beam was reinforced with glass-FRP bars, two beams were reinforced with both glass-FRP bars and steel and one was reinforced with steel, serving as control specimen. While the steel properties were determined according to Indian codes, the material properties of the GFRP bars used in the project were taken as provided by the manufacturer.

Fig - 1 GFRP Rebar

1.2. FINITE ELEMENT ANALYSIS USING ABAQUS The beams had a load span of 1,800 mm and a rectangular cross section of 150 mm wide and 200 mm high. Two steel bars of 8-mm diameter were used as reinforcement at the compression side of the beam as hanger bar. Steel stirrups with 8-mm diameter and 100mm spacing were used as shear reinforcement. More details of the test beams are shown in Figure 3, and Table 1. Cubic concrete specimens of 150 mm high were cast at the same time as the beams. The average cube strength in compression (fcu) was evaluated by tests on four cubic specimens. Sand-coated GFRP bars used for the tests were manufactured by CSK Technology, Hyderabad. The bar was 16mm in diameter. The tensile strengths and elastic moduli of the GFRP bars are reported in Table 2.

Reinforced concrete is a complicated material to be modeled within finite element packages. A proper material model in the finite element model should be capable of representing both the elastic and plastic behavior of concrete in compression and tension. The complete compressive behavior should include both elastic and inelastic behavior of concrete. The development of a finite element model (FEM) may need intensive material testing to incorporate into the material model in any of the finite element (FE) packages available (Sinaei et al., 2011.In this paper, the ABAQUS program is used to model the behavior of Concrete beams reinforced with hybrid bars. The finite element model uses the concrete damaged plasticity

Table - 1 : Details of Tested Beams Description Steel GFRP GFRP and Steel GFRP and Steel SRC GFRP GS – 1 GS – 2

Beam SRC GFRP GS - 1 GS - 2

fck (MPa) 30 30 30 30

E (GPa) 27386 27386 27386 27386

ρs 0 0 0.67 1.34

ρf 1.34 1.34 1.34 1.34

ρf / ρs

0.5 1

- Beam reinforced with steel rod only - Beam reinforced with GFRP rod only - Beam reinforced with steel (As) and GFRP (Af) rod for 0.5 Af/As ratio.

- Beam reinforced with steel (As) and GFRP (Af) rod for 1.0 Af/As ratio.

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Table - 2 : Mechanical Properties of GFRP Bars Rebar Diameter (mm) 16

Tensile Strength (MPa) 902

Table-3 : Mix proportion of M30 Grade

Elastic Modulus (GPa) 45

Mix design of M30 This study follows the concrete mix design of IS 102622006 for the design of M30 grade concrete. The mix proportion of M30 grade was shown in Table 3 and the mix ratio was 1: 1.85: 1.72: 0.45

Material

Weight

Unit

Cement content

476.10

Kg/m3

Water content

214.30

Kg/m3

Fine aggregate content

882.03

Kg/m3

Coarse aggregate content

820.50

Kg/m3

2.2 Test Setup and Test Procedure A four-point flexural test was carried out as shown in Figure 2. Linear variable differential transducers (LVDT) were placed at mid-span and at middle third of supports to measure the deflections. Loads were gradually applied

with a hydraulic jack and measured with a load cell. Crack initiation and propagation were examined at each load level. Beam deflection and load values were recorded simultaneously.

Fig - 2 : Tested beams description—instrument and setup

SRC

Fig - 3 : Description of beams cross section

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reinforcement was used as the embedded element and the concrete was designated as the host element.

3.1.2 Concrete The uniaxial compressive strength of concrete selected as: fck = 30 MPa The Poisson ratio of concrete (Ѵ) is taken as 0.2 The Stress – Strain graph of M30 grade concrete for to calculate the young’s modulus as shown in Figure 6.

Fig – 4 : Experimental setup.

Fig - 5 : Reinforcement cage

Fig – 6 : Stress – Strain graph of M30 Grade

3 Finite Element Model in ABAQUS

3.1.3 GFRP Rebar

3.1 Material properties

The GFRP bars used in the reinforced concrete beam were assumed to have the yielding stress (σy) of 920 MPa.

3.1.1 Steel reinforcing bar An elastic, perfectly plastic material was used for the steel bar with an equal behavior in tension and compression (Li et al., 2006). The steel bar was treated as a uniaxial material throughout the element section. We can define the rebars as one-dimensional strain elements that can be embedded in the concrete. Their behavior is same as an elastic-plastic material. The rebars and concrete cracking behavior were considered independently. The steel bars used in the reinforced concrete beam were assumed to have the yielding stress:

The Poisson ratio of concrete (Ѵ) is taken as 0.25.The elastic modulus was assumed to be 45GPa.

3.2 The finite element mesh In order to obtain accurate results from the FE model, all the elements in the model were purposely assigned the mesh size of 10mm to ensure that each two different materials share the same node. The type of mesh selected in the model is structured. The mesh element for concrete is 3D solid which is called C3D8R and for the rebar it is 2D truss which is called T3D2 (Figure 8).

σy = 415 MPa While it’s elastic modulus was assumed to be: E = 200 GPa

3.3 Boundary conditions

The steel reinforcement was assigned with a Poisson’s ratio of 0.3, and full bond contact between the steel reinforcement and concrete was presumed. The embedded element option was used for connecting the reinforcement element to the concrete element, steel

The first boundary condition was assumed as the bottom of the end Plates under the beam was fixed in X, Y and Z – Directions and second boundary condition was as the middle third plates were restrained in X and Z – Directions and Gives displacement in Y – Dir..

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The boundary conditions in ABAQUS model were shown in Figure 10.

Fig - 7 : Beam modeling in ABAQUS

Fig - 11 : ABAQUS Results.

4 Test results and comparisons This chapter describes the analytical and experimental results of all the 4 beam specimens. Out of 4 beams one beam was controlled beam. One beam was reinforced with GFRP and two beams were reinforced with different reinforcement ratio of Af/As.

4.1 Flexural Capacity

Fig - 8 : Meshing of beam in ABAQUS

The Ultimate load carrying capacity of the tested beams are shown in Table 4.The flexural capacity of the hybrid GFRP/steel-reinforced concrete beams increased as the reinforcement ratio increased. From the graphs 11(a,b,c and d), the analytical models have good agreement with experiment results. The comparisons of Ultimate load capacity of beams are shown in Table 4. The ultimate load carrying capacity of GFRP reinforced beam is almost nearer to the steel reinforced beam. The load carrying capacity is increased about 15% with the decrease of Af/As ratio.

Table-4 : Comparison of Ultimate load capacity of beams

Fig - 9 : Assemblage in ABAQUS

Fig - 10 : Boundary conditions in ABAQUS

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Specimens

Theoretical Load (kN)

Experimental Load (kN)

SRC

132.55

119

GFRP

124.34

121

GS – 1

131.22

128

GS - 2

138.89

135

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4.2 Loads vs. Deflection

150

RC

The Load vs. Deflection curve is shown in Figure 12.

From the graph, for the same load, the deflection of GFRP beam is maximum, the deflection of SRC beam is minimum and the deflections of different reinforcement ratios are in between them. The deflection of Hybrid RC beams decreases with the decrease of Af/As.The GFRP reinforced beam is more ductile than steel reinforced beam but decreased with the decrease of Af/As.

LOAD (kN)

100 THE EXP 50

0 0

5 Deflection (mm)10

15

Fig-12(a) :SRC beam

COMPARISON OF LOAD vs. DEFLECTION

150 140

LOAD (kN)

GFRP

120

LOAD (kN)

100

GS - 1 RC

50

GFRP

80

GS - 2

60

THE

40

EXP

0 0

20

5

10 15 Deflection (mm)

20

25

Figure.13 Plot of comparison of load vs. deflection

0 0

5

10 (mm) Deflection

15

20

4.3 Cracks

Fig - 12(b) : GFRP beam

The first crack developed in SRC, GS – 1 and GS – 2 at 30 kN, 21 kN, 24 kN and 28 kN respectively. In SRC beam, GS 1 and GS – 2, the first crack was developed nearer to the center of the beam. In GFRP beam, the first crack was occurred just below the loading point. The cracks patterns developed in concrete beams are shown in (Figure 11). The average crack spacing of RC beams was minimal, the average crack spacing of GFRP beams was maximal, and the average crack spacing of hybrid RC beams was somewhere in the middle. The average crack spacing decreases with the decrease of Af/As.

150

GS - 1 100

LOAD (kN)

100

EXP

50

THE 0 0

5

Deflection 10 (mm)

15

20

Fig - 12(c) : GS - 1 beam 150

GS - 2 LOAD (kN)

100 THE

50

Fig - 14(a) : SRC beam

EXP 0 0

5

Deflection 10 (mm)

15

20

Fig -12(d) : GS - 2 beam Figure.12 Plot of comparison of experimental and analytical values

Fig - 14(b) : GFRP beam

Fig - 14(c) : GS - 1 beam

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Beams Reinforced with FRP Bars”, ASCE, Journal of Composite Construction 2011.15:682-695.

Fig - 14(d) : GS - 2 beam

[5]

Dawid Pawłowskia , Maciej Szumigałaa, “Flexural behaviour of full-scale basalt FRP RC beams – experimental and numerical studies”, Science Direct, Procedia Engineering 108 ( 2015 ) 518 – 525.

[6]

Douglas Tomlinson and Amir Fam, M.ASCE “Performance of Concrete Beams Reinforced with Basalt FRP for Flexure and Shear” in Journal of composites for construction.

[7]

Hsuan-Teh Hu, Fu-Ming Lin, Yih-Yuan Jan, “Nonlinear finite element analysis of reinforced concrete beams strengthened by fiber-reinforced plastics”, Science Direct, Composite Structures 63 (2004) 271–281.

[8]

IS: 10262- 2009, “Concrete Mix ProportioningGuidelines”.

5. CONCLUSIONS Based on the experimental results and predicted models, have drawn the following conclusions: 1. A Glass-FRP-reinforced beam behaved linearly until cracking and almost behaves linearly between cracking and failure, with a greatly reduced slope. At failure, the beam was largely deflected.

2. The ultimate load carrying capacity of GFRP reinforced beam is almost nearer to the steel reinforced beam. The load carrying capacity is increased about 15% with the decrease of Af/As ratio.

3. For the same load, the deflection of GFRP beam is maximal, the deflection of SRC beam is minimal and the deflections of GFRP-Steel reinforced beams are between them. The deflection of GFRPSteel reinforced beams decreases with the decrease of Af/As. 4. The predicted load vs. deflection behavior from ABAQUS was in good agreement with the experimental results.

[9] IS: 456-2000, “Indian Standard Plain and Reinforced concrete - Code of Practice”.

REFERENCES [1]

Achillides, Z., and Pilakoutas, K. (2004). “Bond behavior of fiber reinforced polymer bars under direct pullout conditions.”

J. Compos.

Constr., 10.1061/(ASCE)1090-0268(2004)8:2(173), 173–181.

[2]

Ahmed El Refai, Ph.D., P.E.; Mohamed-Amine Ammar; and Radhouane Masmoudi “Bond Performance of Basalt Fiber-Reinforced Polymer Bars to Concrete” in Journal of composites for construction.

[10]

Xiaoshan Lin(1) and Y. X. Zhang, “Novel Composite Beam Element with Bond-Slip for Nonlinear FiniteElement Analyses of Steel/FRP-Reinforced Concrete Beams”, ASCE, Journal of Structural Eng.

[11]

Zhang, Y. X., and Lin, X. (2013). “Nonlinear finite element analyses of steel/FRP-reinforced concrete beams by using a novel composite beam element.”

Adv. Struct. Eng., 16(2), 339–352.

[12] Ze-Yang Sun(1); Gang Wu(2); Zhi-Shen Wu, M.ASCE3; and Jian Zhang, “Nonlinear Behavior and Simulation of Concrete Columns Reinforced by Steel-FRP Composite Bars”, ASCE, Journal of Bridge Eng. 2014.19:220-234.

[3] Brahim Benmokrane(1); Fareed Elgabbas(2); Ehab A. Ahmed, M(3); and Patrice Cousin(4), “Characterization and Comparative Durability Study of Glass/Vinylester, Basalt/Vinylester, and Basalt/Epoxy FRP”, ASCE, Journal of Composite Construction.

[4]

Chakib Kassem(1); Ahmed Sabry Farghaly(2); and Brahim Benmokrane(3), “Evaluation of Flexural Behavior and Serviceability Performance of Concrete

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